The anti-atherosclerotic effect of three drugs of current interest have been tested in the cynomolgus monkey. These drugs include ethane-hydroxy-diphosphonate (EHDP), dichloro-methylene-diphosphonate (Cl2MDP) and sodium p-hexadecylaminobenzoate (PHB). Of these drugs only sodium p-hexadecylaminobenzoate (PHB) showed significant protective action against the development of atherosclerosis. It is now planned to compare the effects of these 3 drugs on the regression of atherosclerosis in the cynomolgus monkey.